1. Field of the Invention
The present invention relates to a robot control system, in particular, relating to a robot control system provided with a function of changing the criterion for communication quality in accordance with the distance between a machine and a portable wireless operation panel.
2. Description of the Related Art
A portable operation panel for teaching a robot is required to satisfy the standard (ISO 10218-1) that the operation panel can output signals to perform an emergency stop of the robot so as to be able to promptly stop the robot in an emergency. When a portable operation panel is used based on wireless communication, there is a risk that the robot cannot be stopped promptly if the quality of the wireless communication is low, and hence is hazardous. For this reason, it has been a practice that the robot is stopped when the quality of wireless communication becomes lower than a certain level to thereby ensure safety.
However, the communication quality of wireless communication may be degraded by environmental influences such as the existence of obstacles, other wireless communications and the like, hence it is inconvenient if the criterion for stopping the robot due to the communication quality is strict. On the other hand, if the criterion is loosened, there is a risk that a long time is taken to correctly transmit an emergency stop signal when teachings and other hazardous tasks are executed, causing safety problems.
As a conventional robot control system, there has been a known system which ensures safety by recognizing the position of the operator (e.g., Japanese Patent No. 5492438). However, this disclosure in no way refers to the feature that the criterion for communication quality is changed.
As a wireless teaching device, there has been a known automated machine system which, by exchanging live signals by wireless communication at predetermined intervals and monitoring the time interval of reception so as to detect the wireless communication state, gives warnings to the operator and stops the automated machine when the wireless communication state becomes poor (Japanese Unexamined Patent Publication (Kokai) No. 2007-233817). This conventional art refers to a technique of confirming communication quality based on the interval between live signals to just give a warning or stop the system when the interval exceeds a certain level. That is, this conventional art does not include any reference to changing the criterion for communication quality depending on a distance. There is a description that parameters are introduced so as to adjust the criterion. That is, the criterion is assumed to be simply adjusted by the operator after grasping the current communication quality. However, there is no reference to using a method based on an automatic change of the criterion in accordance with some physical quantities.
There is another known automated machine system which, by monitoring the intensity of radio waves between the controller and the teaching device, gives warnings and/or stops the automated machine when the intensity of radio waves becomes equal to or lower than a predetermined threshold value (for example, International Publication 2006/103838). FIG. 1 shows a configuration of a conventional automated machine system. A conventional automated machine system 1000 is adapted to stop a robot 1001 when the quality of communication between a transceiver 1021 of a control device 1002 for controlling the robot 1001 and a transceiver 1041 of a teaching device 1004 degrades, to thereby ensure safety.
For example, as shown in FIG. 1, data (live data: dL) for confirming that radio communication is performed correctly is exchanged every fixed period of time. When communication quality is good, live data dL can be received in the fixed period from time t1 to t2. Under such a circumstance, the robot 1001 is operated. On the other hand, when dL can be received at time t1 but cannot be received at time t2, a warning is generated or the robot 1001 is stopped. However, despite the fact that the operator is kept a certain distance apart from the robot and in safety, if wireless communication degrades, the robot is promptly stopped, giving rise to inconvenience.